1. Field of Invention.
This invention relates to an improved scan controller for imaging devices that acquire tomographic images of a subject by using nuclear magnetic resonance (NMR); and more particulary, to such a scan controller having an improved memory performance for scan control signals.
2. Description of the Prior Art.
The NMR imaging device comprises a magnetic assembly including a static magnetic field coil to generate a uniform static magnetic field, and a gradient magnetic field coil to generate in the same magnetic field as the static magnetic field straight and gradient magnetic fields in the X, Y, and Z directions. Also included are transmitting and receiving sections to detect NMR signals from the subject by applying a high-frequency radio frequency (RF) pulse to the magnetic field generated by the magnetic assembly, and a control and image processing section to control the transmitting/receiving sections and magnetic assembly, and process the detected data for image display.
When controlled by the control and image processing section, this NMR imaging device sequentially outputs high-frequency pulses based on the Saturation Recovery (SR) method or the Inversion Reconvery (IR) method. The control and image processing sections also control the magnetic assembly and transmitting/receiving sections to restore images through sequential data collection based for example, on the Fourier analysis.
The control and image processing section is usually equipped with a scan controller. The scan controller generates a gradient magnetic field and a high-frequency pulse according to the respective operation sequences of the magnetic assembly and transmitting/receiving section. Control signals, used to generate the gradient magnetic field and high-frequency pulse according to desired sequences, are stored in advance, and are read out to execute the desired sequences. Stored control signals have different waveforms, amplitudes, and durations, according to the type of desired sequence.
Therefore, the scan controller requires a large memory capacity to store the numerous consecutive control signals. Furthermore, to enhance the resolution of the control signal amplitude, the digital data must contain a large number of bits to express the amplitude. This, in turn, increases the need for a larger memory capacity.